These data were obtained from tests carried out on a 10-kVA, 2300:230-V, 60-Hz distribution transformer:
• Open-circuit test, with low-voltage winding excited: applied voltage 230 V, current 0.45 A, input power 70 W
• Short-circuit test, with high-voltage winding excited: applied voltage 120 V, current 4.35 A, input power 224 W
(a) Compute the efficiency of the transformer when it is delivering full load at 230 V and 0.85 power factor lagging.
(b) Find the efficiency of the transformer when it is delivering 7.5 kVA at 230 V and 0.85 power factor lagging.
(c) Determine the fraction of rating at which the transformer efficiency is a maximum, and calculate the efficiency corresponding to that load if the transformer is delivering the load at 230 V and a power factor of 0.85.
(d) The transformer is operating at a constant load power factor of 0.85 on this load cycle: 0.85 full load for 8 hours, 0.60 full load for 12 hours, and no load for 4 hours. Compute the transformer's all-day (or energy) efficiency.
(e) If the transformer is supplying full load at 230 V and 0.8 lagging power factor, determine the voltage regulation of the transformer. Also, find the power factor at the high-voltage terminals.